Britain's Prince William stands next to his wife Kate, Duchess of Cambridge, as she leaves the King Edward VII hospital in central London in December. / Alastair Grant, AP

by Maria Puente and Kim Hjelmgaard, USA TODAY

by Maria Puente and Kim Hjelmgaard, USA TODAY

LONDON - At last, after weeks of waiting and on-the-edge anticipation (in a heat wave), the royal baby is ready to arrive. Duchess Kate of Cambridge is in the hospital and in the early stages of labor, Buckingham Palace confirmed early Monday.

"The Duchess traveled by car from Kensington Palace to the Lindo Wing at St. Mary's Hospital with the Duke of Cambridge," tweeted Clarence House, the press office for Prince William and Catherine, the Duke and Duchess of Cambridge.

The couple's spokesman said, "Things are progressing normally" so far.

And not a moment too soon for everyone in the United Kingdom, from the queen and the prime minister down to each of the sweaty members of the media mob waiting for more than two weeks outside St. Mary's Hospital in Paddington.

As soon as the Clarence House tweet went out, the royals media piled onto Twitter.

"Duchess of Cambridge arrived at hospital at 5.45 am (local time). Believed to have used Cambridge wing entrance used by Princess Diana," tweeted David Brown of The Times of London.

"What do you think - a boy or a girl?" is the refrain being heard in and around the streets of Paddington as the world waits for news.

Hospital workers, meanwhile, could be heard saying, "It's just ridiculous," referring to the hundreds of jostling journalists and photographers massed outside of St Mary's early on Monday morning.

Photographers paced back and forth outside the hospital in the mid-morning sun, on another hot day for London. Edward Cumming, 65, was sitting in the shade of a tree across from the entrance to the Lindo Wing.

"For one baby this seems a bit much," he said. "Although I guess you have to expect it for a royal baby."

Cumming, who hopes the monarchy in the U.K. persists for some time, said that the royal birth may help that effort.

Australian tourists Natasha and Diana (no last names or ages at their request) said they have been hanging around in London for about a week waiting for news of the royal birth, before heading to the British beauty spot of Cornwall in the far western edge of the island. When the news broke, they rushed over to see if they could spot anything. They couldn't, and were sitting in a shady spot wondering what to do next.

"We're kind of gutted it's happening today," Natasha said, before the two decided the wait for the baby was going to be too long and started making their way back toward Paddington station.

Kate and husband Prince William, both 31 and about to have their first baby, had been spending time at her parents' mansion about 50 miles away in rural Bucklebury, partly to escape the high temperatures (for London) in the city.

They had returned to Kensington Palace this weekend, according to the British media, although the palace had refused to confirm that, and said nothing until it confirmed she was in the hospital and in labor today.

She checked into the private Lindo Wing (Twitter jokesters had nicknamed it the "Limbo WIng" during what they called #GreatKateWait), where William and brother Prince Harry were born more than three decades ago.

And now everyone waits some more.

The palace said weeks ago that the duchess intends to have a natural birth, although that could change depending on circumstances. But the Cambridge press office is not discussing anything about that, nor whether labor was induced.

British reporters were reminding readers and followers that when William was born at St. Mary's 31 years ago, it was after about 16 hours of induced labor.

The palace had earlier planned to inform the world once she was in the hospital and started labor. As soon as the baby is born, William will call his grandmother, Queen Elizabeth II, on an encrypted call to let her know the news.

However, if the birth is in the middle of the night, he will not wake her up, British media are reporting.

The queen, who returned as per usual to Buckingham Palace today from Windsor Castle where she usually spends weekends (her flag went up over the palace when she arrived), joked this week, in answer to a child's question, that she hoped the baby would arrive soon because she's going on her annual vacation next week to her Balmoral estate in Scotland.

Meanwhile, if it's still daylight, a royal courier will emerge from the hospital and, with a police escort and a news helicopter clattering overhead, will head to Buckingham Palace to post a notice of the baby's gender, size and weight on an easel at the palace front gates. (If the birth is in the middle of the night, this will wait until morning.)

Then the news will flood onto palace websites and social media and TV screens, and the celebrations will commence. Relief that it all went well will mix with joy, and pride that the British monarchy endures with another royal heir in hand.

This baby, whose name we will likely not learn for at least a few more days, will move to third-in-line to the throne, behind William at second and grandfather Prince Charles at first. Great-granny the queen is 87.

A girl would make for an especially historic royal baby, coming into the world with unprecedented expectations. For the first time in a 1,000 years of the English monarchy, the rules of succession have been changed so that birth order will trump gender. This princess of Cambridge, as she will be known, will be a future monarch even if she later has younger brothers.

The anticipation of the birth had built to a fever pitch, in part because it had been expected last weekend and nothing happened. This week, press reports had it, Prime Minister David Cameron, meeting with his Cabinet colleagues, was handed a note and gasped a little. Was it the royal baby? Nope, it was just a cricket score.

Today, he expressed the country's best wishes. "A very exciting occasion and the whole country is excited with them," he said. "So everyone is hoping for the best."

So it's big news for the Brits, certainly, and huge news for the world's ever-growing celebrity media universe, where celeb babies are click-magnets and royal babies even more so.